Field of the Invention
The present invention relates to a scavenged gas amount calculation device for an internal combustion engine, which calculates a scavenged gas amount, and an internal EGR amount calculation device which calculates an internal EGR amount using the scavenged gas amount.
Description of the Related Art
Conventionally, an internal EGR amount calculation device for an internal combustion engine is known as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2004-251182 is known. In this internal EGR amount calculation device, an internal EGR amount is calculated by adding the amount of blown-back gases (blown-back gas amount) to the amount of residual burned gases. The amount of residual burned gases represents the amount of burned gases remaining in a cylinder, and is calculated, specifically, using the equation of state of gas.
Further, the amount of blown-back gases represents the amount of burned gases blown back into the cylinder after the burned gases flows from an exhaust passage into an intake passage due to a pressure difference between the intake passage and the exhaust passage, during a valve overlap time period. The amount of blown-back gases is calculated using a calculation equation to which is applied the nozzle equation by regarding a path through which burned gases flow as a nozzle.
The nozzle equation includes a time-integral value Σ(μA) of an effective opening area. The time-integral value Σ(μA) of the effective opening area is calculated specifically by calculating a crank angle-integral value f1 (OL) by integrating the effective opening area with respect to a crank angle, and dividing the crank angle-integral value f1 (OL) by a rotational speed NE of the engine.
As mentioned hereinabove, the blown-back gases are produced during the valve overlap time period due to a pressure difference between the intake passage and the exhaust passage, and hence depending on the relationship between a pressure within the intake passage (hereafter referred to as “the intake pressure”) and a pressure within the exhaust passage (hereafter referred to as “the exhaust pressure”), it sometimes occurs that the amount of blown-back gases decreases or no blown-back gases are produced. For example, in a case where the valve overlap time period is relatively long, when the engine is in high-load operation or when the engine is a supercharger-equipped engine, which is performing supercharging, the intake pressure sometimes becomes higher than the exhaust pressure. In such a case, burned gases in the cylinder are scavenged into the exhaust passage by air flowing into the cylinder. Hereafter, burned gases which are scavenged from within the cylinder into the exhaust passage are referred to as “scavenged gases”. The internal EGR amount disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2004-251182 does not take such scavenged gases into account, and hence under conditions where scavenged gases are produced, the calculation accuracy of the internal EGR amount is reduced.